PROJECT SUMMARY Underage drinking in the United States is a serious health concern, with a multifaceted etiology and wide- ranging implications including risky situations (motor vehicle accidents, risky sex, and violence) and alcohol use disorder (adolescents have the highest rate of alcohol use disorder onset). Both environmental and individual characteristics are implicated in the development of adolescent drinking behavior. At the environmental level, social, locational, and situational context characteristics influence adolescent patterns of drinking. At the individual level, one of the strongest individual predictors of underage drinking is behavioral undercontrol (BU; e.g. impulsivity, sensation seeking). Interventions that target differences in BU successfully delay onset and reduce quantity of alcohol use in underage drinkers. However, research has shown that context characteristics, and differences in BU, meaningfully change drinking behavior. Hence, there is an opportunity to investigate how context effects differ by sex and are moderated by BU to produce heavy episodic drinking at the event level; by conducting time-sensitive research investigating how BU predicts self- selection into drinking contexts, and how BU subsequently moderates the impact of those contexts. This K01 proposal, titled ?Informing treatment adaptation using fine-grained context data in adolescent alcohol use? proposes to collect fine-grained data that could inform context-sensitive interventions, by informing when, where, and with whom to intervene, along with adaptation to sex- or context-specific situations. Equal numbers of male and female adolescents (N = 120, ages 15-17 years) who report at least one heavy drinking episode in the past two weeks, will be recruited for a 17-day ecological momentary assessment (EMA) survey preceded by a single laboratory session. The laboratory session will include self-report and behavioral assessments of BU as well as environmental factors. The EMA will include random user prompts as well as self-initiated reports assessing alcohol use, social, locational, and situational context characteristics, along with assessments of BU prior to, and after, alcohol use. The project has three specific research aims: 1) Examine whether context mediates the effect of BU on adolescent drinking. 2) Examine whether BU moderates the role of context in predicting adolescent drinking. 3) Examine how drinking impacts impulsivity, and how this impact predicts alcohol consequences. By informing context-sensitive interventions based on findings, we will capitalize on technology that allows for context-appropriate prompts (?Just-in-time? interventions). The associated training plan will provide the candidate with the ability to independently conduct EMA surveys among adolescents and aid in securing future funding, becoming a substantive expert on event-level context characteristics and individual traits using fine-grained assessment tools, and informing treatment adaptations for individual-differences-based interventions. Thus, the project is aligned at multiple levels with NIAAA?s underage drinking research initiative into investigating factors that drive harmful adolescent alcohol use.